Text-to-speech (TTS) systems convert written text into sound. This conversion may be useful to assist users of digital text media by synthesizing speech representing text displayed on a computer screen. Speech-recognition systems have progressed to a point at which humans may interact with and control computing devices by voice. TTS and speech recognition, combined with natural language understanding processing techniques, enable speech-based user control and output of a computing device to perform tasks based on the user's spoken commands. The combination of speech recognition and natural-language understanding processing is referred to herein as speech processing. TTS and speech processing may be used by computers, hand-held devices, telephone computer systems, kiosks, and a wide variety of other devices to improve human-computer interactions.